Power supply control device and communication device

ABSTRACT

A power supply control device includes: a power generator that converts energy into power; an environmental sensor that detects a state of an ambient environment; and a controller that controls an operation timing of a functional circuit that operates upon receipt of power supplied from the power generator based on the state of the ambient environment detected by the environmental sensor.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of and claims the benefit of priorityof U.S. patent application Ser. No. 16/270,380, filed Feb. 7, 2019,which in turn claims priority to Japanese Patent Application No.2018-34499, filed on Feb. 28, 2018, the entire contents of each of whichare incorporated herein by reference.

FIELD

The disclosed technology relates to a power supply control device and acommunication device.

BACKGROUND

For example, the use control of power obtained by a power generationelement such as a solar cell is performed.

Related art is disclosed in Japanese Examined Utility Model(Registration) Application Publication No. 62-24997, Japanese Laid-openPatent Publication No. 2006-204024 and Japanese Unexamined Utility Model(Registration) Application Publication No. 62-041349.

SUMMARY

According to an aspect of the embodiments, a power supply control deviceincludes: a power generator that converts energy into power; anenvironmental sensor that detects a state of an ambient environment; anda controller that controls an operation timing of a functional circuitthat operates upon receipt of power supplied from the power generatorbased on the state of the ambient environment detected by theenvironmental sensor.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a graph illustrating an example of an output characteristicof a solar cell when illuminance of light applied to the solar cell ischanged;

FIG. 1B is a graph illustrating an example of the output characteristicof the solar cell when an ambient temperature is changed;

FIG. 2 is a graph illustrating an example of a temperaturecharacteristic of an electrostatic capacity of a capacitor;

FIG. 3A is a diagram illustrating an example of a configuration of apower supply control device according to a first embodiment of thedisclosed technology;

FIG. 3B is a diagram illustrating an example of a configuration of thepower supply control device according to the first embodiment of thedisclosed technology;

FIG. 4 is a flowchart illustrating an example of a flow of processingperformed in a control unit according to the first embodiment of thedisclosed technology;

FIG. 5 is a diagram illustrating an example of a configuration of thepower supply control device according to the first embodiment of thedisclosed technology;

FIG. 6 is a flowchart illustrating an example of a flow of processingperformed in a control unit according to a second embodiment of thedisclosed technology;

FIG. 7 is a diagram illustrating an example of a configuration of apower supply control device according to a third embodiment of thedisclosed technology;

FIG. 8 is a diagram illustrating an example of a configuration of apower supply control device according to a fourth embodiment of thedisclosed technology;

FIG. 9 is a flowchart illustrating an example of a flow of processingperformed in a control unit according to a fourth embodiment of thedisclosed technology;

FIG. 10 is a diagram illustrating an example of a configuration of apower supply control device according to a fifth embodiment of thedisclosed technology;

FIG. 11 is a diagram illustrating an example of a configuration of apower supply control device according to a sixth embodiment of thedisclosed technology; and

FIG. 12 is a diagram illustrating an example of a configuration of acommunication device according to a seventh embodiment of the disclosedtechnology.

DESCRIPTION OF EMBODIMENTS

For example, there is known a power supply device including a solarcell, a main battery, and a control circuit that intermittently suppliesa battery voltage to an equipment and controls a time interval at whichthe battery voltage is supplied to the equipment. In this power supplydevice, the control circuit supplies a battery voltage to the equipmentfrom the main battery when a voltage of the solar cell reaches a certainlevel or lower, and performs control to increase the time interval whenthe voltage of the solar cell reaches the certain level or reaches thecertain level or lower.

There is known a power supply control method in which a generator and abattery are prepared as a power supply of an electronic equipment inwhich a standby state and an operating state may be switched, the methodincluding supplying power from the generator when power may be suppliedfrom the generator, and supplying power from the battery when power maynot be supplied from the generator. In this method, when the powersupply is continuously performed by the battery and then a predeterminedperiod of time elapses, an operation mode of the electronic equipment isset to the standby state, and when the power supply by the generatorbecomes possible, the operation mode is returned to a normal operation.

There is known a photovoltaic power generation system having a controlcircuit that, when a solar cell generates power, intermittently chargesa secondary battery while intermittently supplying power from a solarcell to a load. In this photovoltaic power generation system, when thesolar cell does not generate power and a charging voltage of thesecondary battery is a predetermined voltage or higher, the controlcircuit intermittently supplies power from the secondary battery to theload.

In recent years, development of a sensor node operated by power obtainedby environmental power generation has been advanced. Power obtained by apower generation element such as a solar cell is very weak, and furthera power generation amount fluctuates with the change of the environment.For this reason, stable supply of power is a problem in the developmentof a sensor node. In order to realize a stable power supply, it is alsoconceivable to accumulate the surplus of power generated by the powergeneration element in a storage element.

FIG. 1A is a graph illustrating an example of an output characteristicof a solar cell when illuminance of light applied to a solar cell whichis an example of a power generation element is changed. FIG. 1B is agraph illustrating an example of the output characteristic of the solarcell when an ambient temperature is changed. As illustrated in FIG. 1Aand FIG. 1B, the output characteristic (power generation performance) ofthe solar cell fluctuates according to ambient illuminance andtemperature.

On the other hand, FIG. 2 is a graph illustrating an example of atemperature characteristic of an electrostatic capacity of a capacitorwhich is an example of a storage element. As illustrated in FIG. 2, theelectrostatic capacity (storage performance) of the capacitor fluctuatesaccording to the ambient temperature.

In this manner, a power generation performance of the power generationelement and a storage performance of the storage element fluctuateaccording to an ambient environment. Therefore, when a usage mode of thepower that has been generated or stored is fixed irrespective of theambient environment, there is a risk that the sensor node may becomeinoperable for a long time due to insufficient power and planned datacollection using sensor nodes becomes difficult.

In one aspect, the disclosed technology aims to appropriately use powergenerated in a power generation unit in a system including the powergeneration unit.

Hereinafter, embodiments of the present invention will be described withreference to the drawings. In each of the drawings, the same orequivalent constituent elements and parts are given the same referencenumerals, and redundant explanation will be omitted as appropriate.

First Embodiment

FIG. 3A is a diagram illustrating an example of a configuration of apower supply control device 1 according to a first embodiment of thedisclosed technology.

The power supply control device 1 includes a power generation unit 10, acapacitor 12, a power supply monitoring unit 20, an environmental sensor30, a first timer 41, a second timer 42, a control unit 50, and switches21 and 51. In FIG. 3A, a functional unit 60 that operates with powersupplied from the power supply control device 1 is illustrated togetherwith the power supply control device 1.

The power generation unit 10 converts energy such as light, heat,vibration, radio waves and the like into power and outputs a generatedvoltage. Hereinafter, a case where a solar cell 11 is used as the powergeneration unit 10 will be described as an example, but it is alsopossible to use, as the power generation unit 10, a power generationelement other than the solar cell.

The solar cell 11 has a positive electrode coupled to a power supplyline L_(plus) on a positive side, and a negative electrode coupled to apower supply line L_(minus) on a negative side. The power supply lineL_(minus) on the negative side may be a ground line. The generatedvoltage output from the solar cell 11 is applied to the power supplylines L_(plus) and L_(minus).

The switch 21 is provided on the power supply line L_(plus). The switch21 is turned on or off in accordance with a control signal a1 suppliedfrom the power supply monitoring unit 20. The switch 21 divides thepower supply line L_(plus) into a solar cell side and a load side.

The capacitor 12 is connected in parallel to the solar cell 11. Forexample, the capacitor 12 has one electrode coupled to the power supplyline L_(plus) on the solar cell side, and the other electrode coupled tothe power supply line L_(minus). The capacitor 12 accumulates powergenerated by the solar cell 11.

The power supply monitoring unit 20 controls on/off of the switch 21based on a level of a voltage VDD generated between the power supplyline L_(plus) on the solar cell side and the power supply lineL_(minus). When the level of the voltage VDD exceeds a level of athreshold voltage VH1, the power supply monitoring unit 20 outputs thecontrol signal at for turning on the switch 21. The level of thethreshold voltage VH1 is set to a voltage level at which all of theenvironmental sensor 30, the first timer 41, the second timer 42, thecontrol unit 50, and the functional unit 60 may operate. On the otherhand, when the level of the voltage VDD is equal to or lower than thelevel of a threshold voltage VL1 (VH1), the power supply monitoring unit20 outputs the control signal at for turning off the switch 21.

The functional unit 60 includes at least one circuit block having apredetermined function and operates upon receipt of power supplied fromthe solar cell 11. The functional unit 60 may include, for example, asensor constituting a sensor node and a wireless communication circuit(none of which are illustrated).

The switch 51 is provided on a power supply path for supplying power tothe functional unit 60. For example, the switch 51 and the functionalunit 60 are coupled in series. A series circuit including the switch 51and the functional unit 60 is coupled in parallel to the solar cell 11.The switch 51 is turned on or off in accordance with a control signal a5supplied from the control unit 50. When both of the switches 21 and 51are turned on, the functional unit 60 is coupled to the solar cell 11,and operates upon receipt of power supplied from the solar cell 11. Theswitch 51 is not entirely required as long as the functional unit 60 hasan ON/OFF function. In that case, the control unit 50 directly controlsthe functional unit 60.

The environmental sensor 30 is a sensor that detects a state of anambient environment of the power supply control device 1. As theenvironmental sensor 30, for example, at least one of an illuminancesensor and a temperature sensor may be used. The environmental sensor 30outputs a detection signal a2 indicating a state of the detected ambientenvironment. The detection signal a2 output from the environmentalsensor 30 is supplied to the control unit 50.

The first timer 41 outputs a timing signal a3 at a period T1. The secondtimer 42 outputs a timing signal a4 at a period T2 longer than theperiod T1. Each of the timing signals a3 and a4 is supplied to thecontrol unit 50.

The control unit 50 selects one of the timing signals a3 and a4 based onthe detection signal a2 and outputs the control signal a5 for turning onthe switch 51 in synchronization with the selected timing signal. Forexample, the control unit 50 turns on the switch 51 at intervalscorresponding to the selected timing signal. The control unit 50 mayhave a configuration of a microcontroller including a central processingunit (CPU), a memory, and an input/output unit, for example.

The environmental sensor 30, the first timer 41, the second timer 42,and the control unit 50 are connected to the power lines L_(plus) andL_(minus) on the load side. When the switch 21 is turned on, theenvironmental sensor 30, the first timer 41, the second timer 42, andthe control unit 50 are connected to the solar cell 11, and operate uponreceipt of power supplied from the solar cell 11.

As illustrated in FIG. 3B, it is also possible to change the arrangementof the switch 21 and the switch 51. In the example illustrated in FIG.3B, the switch 21 is provided on the power supply line L_(minus), andthe switch 51 is provided between the power supply line L_(minus) andthe functional unit 60.

The operation of the power supply control device 1 will be describedbelow. In the initial state, it is assumed that the switches 21 and 51are turned off.

When the solar cell 11 is irradiated with light, power is generated inthe solar cell 11. The power generated by the solar cell 11 isaccumulated in the capacitor 12. As the illuminance of the light appliedto the solar cell 11 increases, the generation voltage (charging voltageof the capacitor 12) output from the solar cell 11 increases, and thelevel of the voltage VDD generated in the power supply lines L_(plus)and L_(minus) increases. When detecting that the level of the voltageVDD exceeds the level of the threshold voltage VH1, the power supplymonitoring unit 20 outputs the control signal at for turning on theswitch 21. As a result, the switch 21 is turned on, power is supplied tothe environmental sensor 30, the first timer 41, the second timer 42,and the control unit 50, and each of these blocks is activated.

FIG. 4 is a flowchart illustrating an example of the flow of processingexecuted by the control unit 50. Here, a case where the environmentalsensor 30 is an illuminance sensor, the functional unit 60 includes thesensor and the wireless communication circuit (both not illustrated)constituting the sensor node, and the wireless communication circuitperforms data transmission by wireless communication at the time ofoperation will be described as an example.

In step S1, the control unit 50 acquires the detection signal a2indicating ambient illuminance, the detection signal a2 being outputfrom the environmental sensor 30 (illuminance sensor).

In step S2, the control unit 50 determines whether an illuminance Xindicated by the detection signal a2 is higher than a predeterminedthreshold Y.

When determining that the illuminance X is higher than the threshold Y,the control unit 50 selects the timing signal a3 at a short period andturns on the switch 51 at the timing based on the timing signal a3. Forexample, in step S3, the control unit 50 determines whether the timingsignal a3 has been received. When receiving the timing signal a3, instep S5, the control unit 50 supplies to the switch 51 the controlsignal a5 for turning on the switch 51.

On the other hand, in step S2, when determining that the illuminance Xis lower than the threshold Y, the control unit 50 selects the timingsignal a4 at a short period and turns on the switch 51 at the timingbased on the timing signal a4. For example, in step S4, the control unit50 determines whether the timing signal a4 has been received. Whenreceiving the timing signal a4, in step S5, the control unit 50 suppliesto the switch 51 the control signal a5 for turning on the switch 51.

When the switch 51 is turned on, the functional unit 60 is connected tothe solar cell 11 and operates upon receipt of power supplied from thesolar cell 11. When receiving power supplied from the solar cell 11, thefunctional unit 60 performs processing of transmitting data acquired bythe sensor (not illustrated) to the outside from the wirelesscommunication circuit (not illustrated) by wireless communication.

When the processing in the functional unit 60 is completed, the controlunit 50 supplies to the switch 51 the control signal a5 for turning offthe switch 51 in step S6. When the switch 51 is turned off, thefunctional unit 60 is disconnected from the solar cell 11 and enters astopped state (non-operating state). Thereafter, the processing returnsto step S1.

According to the control mode by the control unit 50, when theilluminance X indicated by the detection signal a2 is higher than thethreshold Y, the switch 51 is turned on each time the timing signal a3at a short period is received. Therefore, the wireless communicationcircuit (not illustrated) constituting the functional unit 60 performsdata transmission at intervals corresponding to the period T1 of thetiming signal a3.

On the other hand, when the illuminance X indicated by the detectionsignal a2 is lower than the threshold Y, the switch 51 is turned on eachtime the timing signal a4 at a long period is received. Therefore, thewireless communication circuit (not illustrated) constituting thefunctional unit 60 performs data transmission at intervals correspondingto the period T2 of the timing signal a4.

As illustrated in FIGS. 1A and 1B, the power generation performance ofthe solar cell 11 changes according to the ambient environment. However,by detecting the state of the ambient environment by the environmentalsensor 30, it is possible to estimate the power generation amount of thesolar cell 11 under the relevant environment in real time. According tothe power supply control device 1 of the present embodiment, theoperation timing of the functional unit 60 is controlled in accordancewith the state of the ambient environment detected by the environmentalsensor 30. Therefore, the power usage amount in the functional unit 60may be adapted to the power generation amount of the solar cell 11 underthe relevant environment. Therefore, it is possible to avoidinoperability of the functional unit 60 over a long period of time dueto power shortage. By using the environmental sensor 30, as comparedwith the case of detecting the power generation voltage of the solarcell, it is possible to more accurately estimate the amount of powergeneration in the solar cell 11, the amount of power generation changingdepending on the ambient environment. Thus, it is possible to moreaccurately control the operation timing of the functional unit 60.

As described above, according to the power supply control device 1 ofthe present embodiment, it is possible to appropriately use the powergenerated in the power generation unit 10 (solar cell 11).

In the above description, the illuminance sensor is used as theenvironmental sensor 30 as an example, but the temperature sensor may beused as the environmental sensor 30. In this case, one of the timingsignals a3 and a4 is selected depending on whether the temperatureindicated by the detection signal a2 output from the temperature sensoris higher than a predetermined threshold. For example, for a temperatureat which the amount of generated power in the solar cell 11 relativelyincreases, the timing signal a3 at a short period is selected, and thefunctional unit 60 is operated at intervals corresponding to the periodT1 of the timing signal a3. On the other hand, for a temperature atwhich the amount of generated power in the solar cell 11 relativelydecreases, the timing signal a4 at a long period is selected, and thefunctional unit 60 is operated at intervals corresponding to the periodT2 of the timing signal a4. The environmental sensor 30 may include anilluminance sensor and a temperature sensor.

In the above description, a mode in which the power generation amount inthe solar cell 11 is estimated based on the detection signal a2 outputfrom the environmental sensor 30 and the operation timing of thefunctional unit 60 is controlled so as to adapt to the estimated powergeneration amount is exemplified. However, the disclosed technology isnot limited to this mode. For example, based on the detection signal a2output from the environmental sensor 30, an electrostatic capacity ofthe capacitor 12 in the relevant environment may be estimated and theoperation timing of the functional unit 60 may be controlled so as toadapt to the estimated electrostatic capacity.

Second Embodiment

FIG. 5 is a diagram illustrating an example of a configuration of apower supply control device 1A according to a second embodiment of thedisclosed technology. The power supply control device 1A is differentfrom the power supply control device 1 (see FIG. 3A) according to thefirst embodiment in that the power supply control device 1A does nothave the second timer 42.

Similarly to the power supply control device 1 according to the firstembodiment, the power supply control device 1A operates the functionalunit 60 at one of a plurality of mutually different intervals based onthe state of the ambient environment detected by the environmentalsensor 30. When operating the functional unit 60 at relatively shortintervals, the power supply control device 1A turns on the switch 51 atintervals corresponding to the period T1 of the first timer 41. On theother hand, when operating the functional unit 60 at relatively longintervals, the power supply control device 1A turns on the switch 51 atintervals corresponding to N times the period T1 of the timing signal a3output from the first timer 41.

FIG. 6 is a flowchart illustrating an example of a flow of processingperformed in the control unit 50 according to the second embodiment ofthe disclosed technology. Here, a case where the environmental sensor 30is an illuminance sensor, the functional unit 60 includes the sensor andthe wireless communication circuit (both not illustrated) constitutingthe sensor node, and the wireless communication circuit performs datatransmission by wireless communication at the time of operation will bedescribed as an example.

In step S11, the control unit 50 determines whether the timing signal a3has been received. When receiving the timing signal a3, in step S12, thecontrol unit 50 acquires the detection signal a2 indicating the ambientilluminance output from the environmental sensor 30.

In step S13, the control unit 50 determines whether the illuminance Xindicated by the detection signal a2 is higher than the predeterminedthreshold Y.

When determining that the illuminance X is higher than the threshold Y,the control unit 50 turns on the switch 51 at the timing based on thetiming signal a3. For example, the control unit 50 having received thetiming signal a3 in step S11 supplies to the switch 51 the controlsignal a5 for turning on the switch 51 in step S14.

On the other hand, in step S13, when determining that the illuminance Xis lower than the threshold Y, the control unit 50 turns on the switch51 at intervals corresponding to N times the period T1 of the timingsignal a3. For example, in step S16, the control unit 50 determineswhether the number of times of receiving the timing signal a3 hascontinuously reached N times. When determining that the number of timesof receiving the timing signal a3 has continuously reached N times, instep S14, the control unit 50 supplies the control signal a5 for turningon the switch 51 to the switch 51, and resets the count of the number oftimes of receiving the timing signal a3.

When the switch 51 is turned on, the functional unit 60 is coupled tothe solar cell 11 and operates upon receipt of power supplied from thesolar cell 11. When receiving power supplied from the solar cell 11, thefunctional unit 60 performs processing of transmitting data acquired bythe sensor (not illustrated) to the outside from the wirelesscommunication circuit (not illustrated) by wireless communication.

When the processing in the functional unit 60 is completed, the controlunit 50 supplies to the switch 51 the control signal a5 for turning offthe switch 51 in step S15. When the switch 51 is turned off, thefunctional unit 60 is disconnected from the solar cell 11 and enters astopped state (non-operating state). Thereafter, the processing returnsto step S11.

According to the control mode by the control unit 50, when theilluminance X indicated by the detection signal a2 is higher than thethreshold Y, the switch 51 is turned on each time the timing signal a3is received. Therefore, the wireless communication circuit (notillustrated) constituting the functional unit 60 performs datatransmission at intervals corresponding to the period T1 of the timingsignal a3.

On the other hand, when the illuminance X indicated by the detectionsignal a2 is lower than the threshold Y, the switch 51 is turned on eachtime the timing signal a3 is continuously received N times. Therefore,the wireless communication circuit (not illustrated) constituting thefunctional unit 60 performs data transmission at intervals correspondingto N times the period T1 of the timing signal a3.

In this way, by using only the timing signal a3 output from the firsttimer 41, it is possible to reduce the circuit scale as compared withthe power supply control device 1 (FIG. 3A) according to the firstembodiment. The power supply control device may include three or moretimers. In this case, based on the state of the ambient environmentdetected by the environmental sensor 30, the control unit 50 selects oneof the timing signals output from each of the plurality of timers andoperates the functional unit 60 at intervals corresponding to theselected timing signal.

Third Embodiment

FIG. 7 is a diagram illustrating an example of a configuration of apower supply control device 1B according to a third embodiment of thedisclosed technology. The power supply control device 1B is differentfrom the power supply control device 1 (see FIG. 3A) according to thefirst embodiment in that the power supply control device 1B furtherincludes a power supply monitoring unit 70, a switch 71, a diode 72, anda power storage unit 73. In the case where the switch 71 includes, forexample, a metal-oxide-semiconductor field-effect transistor (MOSFET),the diode 72 may be a parasitic diode associated with this MOSFET.

Each of the power storage unit 73 and the switch 71 is provided on abranch line L_(b) when coupled to the power supply lines L_(plus) andL_(minus). The branch line L_(b) has one end coupled to the power supplyline L_(plus) on the load side and the other end coupled to the powersupply line L_(minus). For example, a series circuit including theswitch 71 and the power storage unit 73 is coupled in parallel to thesolar cell 11.

The power storage unit 73 is configured by a storage element having alarger storage capacity than the capacitor 12 such as a secondarybattery, a super capacitor, or the like. When both of the switch 21 andthe switch 71 are turned on, the power storage unit 73 is coupled to thesolar cell 11, and charging is performed in the power storage unit 73.

The switch 71 is turned on or off in accordance with a control signal a6supplied from the power supply monitoring unit 70. The diode 72 iscoupled in parallel to the switch 71. For example, the diode 72 has ananode coupled to a positive electrode of the power storage unit 73, anda cathode coupled to the power supply line L_(plus) on the load side.

The power supply monitoring unit 70 controls on/off of the switch 71based on the level of the voltage VDD generated between the power supplyline L_(plus) on the load side and the power supply line L_(minus). Whenthe level of the voltage VDD exceeds the level of a threshold voltageVH2, the power supply monitoring unit 70 outputs the control signal a6for turning on the switch 71. The level of the threshold voltage VH2 isset to a level higher than the level of the threshold voltage VL1 in thepower supply monitoring unit 20. On the other hand, when the level ofthe voltage VDD is lower than the level of a threshold voltage VL2(<VH2), the power supply monitoring unit 70 outputs the control signala6 for turning off the switch 71.

The operation of the power supply control device 1B will be describedbelow. In the initial state, it is assumed that the switches 21 and 51are turned off.

When the solar cell 11 is irradiated with light, power is generated inthe solar cell 11. The power generated by the solar cell 11 isaccumulated in the capacitor 12. As the illuminance of the light appliedto the solar cell 11 increases, the generated voltage (charging voltageof the capacitor 12) output from the solar cell 11 increases and thevoltage VDD generated in the power supply lines L_(plus) and L_(minus)increases. When detecting that the level of the voltage VDD exceeds thelevel of the threshold voltage VH1, the power supply monitoring unit 20outputs the control signal at for turning on the switch 21. As a result,the switch 21 is turned on, power is supplied to the environmentalsensor 30, the first timer 41, the second timer 42, and the control unit50, and each of these blocks starts operating. Similarly to the powersupply control device 1 according to the first embodiment, the controlunit 50 controls the operation timing of the functional unit 60 based onthe state of the ambient environment detected by the environmentalsensor 30.

When detecting that the level of the voltage VDD exceeds the level ofthe threshold voltage VH2 (>VL1), the power supply monitoring unit 70outputs the control signal a6 for turning on the switch 71. As a result,the switch 71 is turned on. When both of the switch 21 and the switch 71are turned on, the power storage unit 73 is coupled to the solar cell 11and the capacitor 12, and is charged with power generated by the solarcell 11.

Since the power storage unit 73 has a larger storage capacity than thecapacitor 12, the level of the voltage VDD lowers as an electric chargemoves from the capacitor 12 to the power storage unit 73. When detectingthat the level of the voltage VDD is lower than the level of thethreshold voltage VL2 (<VH2), the power supply monitoring unit 70outputs the control signal a6 for turning off the switch 71. When theswitch 71 is turned off, the power storage unit 73 is disconnected fromthe solar cell 11 and the capacitor 12. In the case where the powergeneration amount in the solar cell 11 is relatively large, when theswitch 71 is turned off, the level of the voltage VDD increases again.As a result, the switch 71 repeats the on/off operation.

While the on/off operation is repeated in the switch 71, the chargingvoltage of the power storage unit 73 gradually increases. When theamount of power generation in the solar cell 11 is relatively large, aslong as the charging voltage of the power storage unit 73 does notexceed the threshold voltage VL2, the on/off operation in the switch 71continues. By repeating the on/off operation in the switch 71, chargingof the power storage unit 73 is performed intermittently.

When the intensity of light applied to the solar cell 11 decreases, thepower generation amount per unit time of the solar cell 11 decreases,and the level of the voltage VDD decreases.

When detecting that the level of the voltage VDD is lower than the levelof the threshold voltage VL1, the power supply monitoring unit 20outputs the control signal a1 for turning off the switch 21. As aresult, the switch 21 is turned off. Since the power storage unit 73 isintermittently charged, the power supply monitoring unit 20 may detectthe level of the voltage VDD corresponding to the power generationvoltage of the solar cell 11 without being affected by the chargingvoltage of the power storage unit 73. When the switch 21 is turned off,power supply from the solar cell 11 to each block (the environmentalsensor 30, the first timer 41, the second timer 42, the control unit 50,the functional unit 60, and the power supply monitoring unit 70) isblocked.

Similarly, when detecting that the level of the voltage VDD is lowerthan the level of the threshold voltage VL2, the power supply monitoringunit 70 outputs the control signal a6 for turning off the switch 71. Asa result, the switch 71 is turned off. The power accumulated in thepower storage unit 73 is supplied to each block (the environmentalsensor 30, the first timer 41, the second timer 42, the control unit 50,the functional unit 60, and the power supply monitoring unit 70) via thediode 72. In some cases, the power supply monitoring unit 70 turns onthe switch 71 that is SW, again according to the supplied level.

As described above, according to the power supply control device 1Baccording to the present embodiment, even when power generation by thesolar cell 11 is stopped such as at night, each of the above-mentionedblocks (the environmental sensor 30, the first timer 41, the secondtimer 42, the control unit 50, the functional unit 60, and the powersupply monitoring unit 70) may be operated by the power accumulated inthe power storage unit 73.

In the above description, a mode in which the power generation amount inthe solar cell 11 is estimated based on the detection signal a2 outputfrom the environmental sensor 30 and the operation timing of thefunctional unit 60 is controlled so as to adapt to the estimated powergeneration amount is exemplified. However, the disclosed technology isnot limited to this mode. For example, the storage performance(electrostatic capacity) of the power storage unit 73 may be estimatedbased on the detection signal a2 output from the environmental sensor30, and the operation timing of the functional unit 60 may be controlledso as to adapt to the estimated storage performance.

Fourth Embodiment

FIG. 8 is a diagram illustrating an example of a configuration of apower supply control device 1C according to a fourth embodiment of thedisclosed technology. The power supply control device 1C is differentfrom the power supply control device 1 (see FIG. 3A) according to thefirst embodiment in that the power supply control device 1C includes aswitch 80.

The switch 80 is provided on each power supply path for supplying powerto the environmental sensor 30, the first timer 41, and the functionalunit 60. The switch 80 is turned on or off in accordance with a controlsignal a8 supplied from the control unit 50. Each of the environmentalsensor 30, the first timer 41, and the functional unit 60 is coupled tothe solar cell 11 when both of the switches 21 and 80 are turned on, andis activated upon receipt of power supplied from the solar cell 11.

FIG. 9 is a flowchart illustrating an example of a flow of processingperformed in the control unit 50 according to a fourth embodiment of thedisclosed technology. Here, a case where the environmental sensor 30 isan illuminance sensor, the functional unit 60 includes a sensor and awireless communication circuit (both not illustrated) constituting asensor node, and the wireless communication circuit performs datatransmission by wireless communication at the time of operation will bedescribed as an example. Furthermore, in the initial state, it isassumed that the switches 21 and 80 are turned off.

When the level of the voltage VDD generated in the power supply linesL_(plus) and L_(minus) exceeds the level of the threshold voltage VH1,the switch 21 is turned on. When the switch 21 is turned on, the controlunit 50 is activated (step S31).

In step S32, the control unit 50 outputs the control signal a8 forturning on the switch 80. When the switch 80 is turned on, theenvironmental sensor 30, the first timer 41, and the functional unit 60are activated. At the time of activation, the functional unit 60performs a predetermined initial setting.

The control unit 50 supplies a control signal instructing the functionalunit 60 to operate in step S33. As a result, the functional unit 60performs processing of transmitting data acquired by the sensor (notillustrated) to the outside from the wireless communication circuit (notillustrated) by wireless communication.

In step S34, the control unit 50 acquires the detection signal a2indicating ambient illuminance, the detection signal a2 being outputfrom the environmental sensor 30.

In step S35, the control unit 50 determines whether the illuminance Xindicated by the detection signal a2 is higher than the predeterminedthreshold Y.

When determining that the illuminance X is higher than the threshold Y,the control unit 50 determines in step S36 whether the timing signal a3has been received. When receiving the timing signal a3, in step S37, thecontrol unit 50 supplies a control signal instructing the functionalunit 60 to operate. As a result, the functional unit 60 performsprocessing of transmitting data acquired by the sensor (not illustrated)to the outside from the wireless communication circuit (not illustrated)by wireless communication. Thereafter, the processing returns to stepS34.

On the other hand, when determining that the illuminance X is lower thanthe threshold Y in step S35, the control unit 50 supplies a timerreservation signal a7 to the second timer 42 in step S38.

In step S39, the control unit 50 outputs the control signal a8 forturning off the switch 80. As a result, the switch 80 is turned off, andpower supply to the environmental sensor 30, the first timer 41, and thefunctional unit 60 is stopped. For example, the functional unit 60enters a system off state in which power is not consumed.

In step S40, the control unit 50 itself also enters the system offstate. On the other hand, the second timer 42 maintains an operatingstate. The second timer 42 supplies the timing signal a4 to the controlunit 50 when a period corresponding to the period T2 has elapsed fromthe time when the timer reservation signal a7 is received.

When the control unit 50 receives the timing signal a4 output from thesecond timer 42 (step S41: affirmative determination), the processingreturns to step S31 and the control unit 50 is reactivated.

According to the power supply control device 1C according to the presentembodiment, when the illuminance X is maintained higher than thethreshold Y (when the amount of power generation per unit time in thesolar cell 11 is relatively large), the processing from step S34 to stepS37 is repeated. Therefore, the functional unit 60 performs datatransmission at intervals corresponding to the period T1 of the timingsignal a3. In this case, the switch 80 maintains an ON state. Thefunctional unit 60 enters a standby state in which power is consumed, atthe time of non-operation where data transmission is not performed. Whenthe functional unit 60 shifts from the standby state to the operatingstate, the initial setting performed at the time of activation of thefunctional unit 60 is not executed.

On the other hand, when the illuminance X is kept lower than thethreshold Y (when the amount of power generation per unit time in thesolar cell 11 is relatively small), the functional unit 60 performs datatransmission processing after the activation, and thereafter, thefunctional unit 60 and the control unit 50 both enter the system offstate. Thereafter, the functional unit 60 and the control unit 50 arereactivated at the timing based on the timing signal a4. Therefore, inthis case, the functional unit 60 performs data transmission atintervals corresponding to the period T2 of the timing signal a4.

Power consumed by the functional unit 60 when the functional unit 60repeats the standby state and the operating state will be considered. Inthe standby state, power is consumed for reasons such as necessity ofholding information held in a memory (not illustrated) constituting thefunctional unit 60. As an operating interval (data transmissioninterval) of the functional unit 60 becomes longer, power consumptionper one piece of processing increases.

Next, power consumed by the functional unit 60 when the functional unit60 repeats the system off state and the operating state will beconsidered. The power consumption of the functional unit 60 in thesystem off state is substantially zero. However, when the functionalunit 60 returns from the system off state and is reactivated, thepredetermined initial setting is performed. In this initial setting, acertain amount of power is consumed and time is taken. On the otherhand, when shifting the functional unit 60 from the standby state to theoperating state, the initial setting is not required.

Taking these circumstances into consideration, when the operatinginterval (data transmission interval) of the functional unit 60 isrelatively short, it is thought to be preferable to set a state of thefunctional unit 60 at the time of non-operation to the standby state inwhich reactivation is not required and power is consumed, to avoid powerconsumption due to reactivation. On the other hand, when the operatinginterval (data transmission interval) of the functional unit 60 isrelatively long, it is thought to be preferable to set a state of thefunctional unit 60 at the time of non-operation to the system off statein which reactivation is required and power is not consumed, to avoidpower consumption in a non-operating period.

According to the power supply control device 1C according to the presentembodiment, when the functional unit 60 operates at relatively shortintervals corresponding to the period T1 of the timing signal a3, astate of the functional unit 60 at the time of non-operation is set tothe standby state in which reactivation is not required and power isconsumed. When the functional unit 60 operates at relatively longintervals corresponding to the period T2 of the timing signal a4, astate of the functional unit 60 at the time of non-operation is set tothe system off state in which reactivation is required and power is notconsumed. In this manner, by switching the state of the functional unit60 at the time of non-operation according to the operating interval ofthe functional unit 60, the power consumption in the functional unit 60may be suppressed, and more preferable use control of power may berealized.

Fifth Embodiment

FIG. 10 is a diagram illustrating an example of a configuration of apower supply control device 1D according to a fifth embodiment of thedisclosed technology. The power supply control device 1D is differentfrom the power supply control device 1C (see FIG. 8) according to thefourth embodiment in that the power supply control device 1D furtherincludes the power supply monitoring unit 70, the switch 71, the diode72, and the power storage unit 73.

The power supply monitoring unit 70, the switch 71, the diode 72, andthe power storage unit 73 are the same as those of the power supplycontrol device 1B according to the third embodiment (see FIG. 7), sothat duplicate descriptions are omitted.

According to the power supply control device 1D according to the presentembodiment, similarly to the power supply control device 1B according tothe third embodiment, even when power generation by the solar cell 11 isstopped such as at night, each of the above-mentioned blocks (theenvironmental sensor 30, the first timer 41, the second timer 42, thecontrol unit 50, the functional unit 60, and the power supply monitoringunit 70) may be operated by the power accumulated in the power storageunit 73. According to the power supply control device 1D according tothe present embodiment, similarly to the power supply control device 1Caccording to the fourth embodiment, since the state of the functionalunit 60 at the time of non-operation is switched according to theoperating interval of the functional unit 60, power consumption in thefunctional unit 60 may be suppressed. Thus, since the electrostaticcapacity of the power storage unit 73 may be reduced, the size of thepower storage unit 73 may be reduced, and the time for charging thepower storage unit 73 may be shortened.

Sixth Embodiment

FIG. 11 is a diagram illustrating an example of a configuration of apower supply control device 1E according to a sixth embodiment of thedisclosed technology. The power supply control device 1E is differentfrom the power supply control device 1B (see FIG. 7) according to thethird embodiment in that the power supply control device 1E includes aswitch 23 and diodes 22 and 24.

The diode 22 is coupled in parallel to the switch 21. In the case wherethe switch 21 includes, for example, a metal-oxide-semiconductorfield-effect transistor (MOSFET), the diode 22 may be a parasitic diodeassociated with this MOSFET.

The switch 23 is provided on the power supply line L_(plus) and iscoupled in series with the switch 21. The switch 23 is turned on or offin accordance with the detection signal a2 supplied from theenvironmental sensor 30. For example, the switch 23 is turned on and offbased on the state of the ambient environment detected by theenvironmental sensor 30. In the case where the environmental sensor 30is, for example, an illuminance sensor, when the ambient illuminanceindicated by the detection signal a2 is equal to or lower than apredetermined value (for example, when it is estimated that the powergeneration amount in the solar cell 11 has become substantially zero),the switch 23 is turned off.

The diode 24 is coupled in parallel to the switch 23 so as to face in adirection reverse to a direction of the diode 22. If the switch 23includes, for example, a MOSFET, the diode 24 may be a parasitic diodeassociated with this MOSFET. At least one of the switch 23 and the diode24 may be provided on the power supply line L_(minus).

According to the power supply control device 1E according to the presentembodiment, the switch 23 may be turned on and off in accordance withthe power generation amount of the solar cell 11. For example, byturning off the switch 23 when there is no power generation in the solarcell 11, it is possible to avoid that the power accumulated in the powerstorage unit 73 is consumed by the solar cell 11.

In the case where there is no power generation in the solar cell 11,when the switch 23 and the diode 24 are not provided, a backflow mayoccur in which a current from the power storage unit 73 flows into thesolar cell 11 via the diode 22. According to the power supply controldevice 1E according to the present embodiment, the diode 24 facing inthe direction reverse to the direction of the diode 22 may avoid abackflow of the current.

Seventh Embodiment

FIG. 12 is a diagram illustrating a configuration of a communicationdevice 2 according to a seventh embodiment of the disclosed technology.The communication device 2 includes the power supply control device 1,and a sensor 81 and a wireless communication unit 82 which operate uponreceipt of power supplied from the power supply control device 1. Forexample, the sensor 81 and the wireless communication unit 82 correspondto the functional unit 60 illustrated in FIG. 3A or the like. When bothof the switch 21 and the switch 51 are turned on, the sensor 81 and thewireless communication unit 82 operate upon reception of power suppliedfrom the power supply control device 1.

For the sensor 81, for example, any sensor such as a temperature sensor,a humidity sensor, an illuminance sensor, a voltage sensor, or the likemay be applied. The wireless communication unit 82 has a function oftransmitting data acquired by the sensor 81 to the outside by wirelesscommunication. The communication device 2 may constitute a sensor nodein a sensor network. The communication device 2 may include any one ofthe power supply control devices 1A, 1B, 1C, 1D, and 1E instead of thepower supply control device 1.

The power supply control devices 1, 1A, 1B, 1C, 1D, and 1E are anexample of a power supply control device in the disclosed technology.The communication device 2 is an example of a communication device inthe disclosed technology. The power generation unit 10 is an example ofa power generation unit in the disclosed technology. The solar cell 11is an example of a solar cell in the disclosed technology. The powersupply monitoring unit 20 is an example of a power supply monitoringunit and a first power supply monitoring unit in the disclosedtechnology. The power supply monitoring unit 70 is an example of asecond power supply monitoring unit in the disclosed technology. Theswitches 51 and 80 are an example of a first switch in the disclosedtechnology. The switch 21 is an example of a second switch in thedisclosed technology. The switch 71 is an example of a third switch inthe disclosed technology. The switch 23 is an example of a fourth switchin the disclosed technology. The environmental sensor 30 is an exampleof an environmental sensor in the disclosed technology. The timer 41 isan example of a first timer in the disclosed technology. The timer 42 isan example of a second timer in the disclosed technology. The controlunit 50 is an example of a control unit in the disclosed technology. Thefunctional unit 60 is an example of a functional unit in the disclosedtechnology. The power storage unit 73 is an example of a power storageunit in the disclosed technology.

All examples and conditional language provided herein are intended forthe pedagogical purposes of aiding the reader in understanding theinvention and the concepts contributed by the inventor to further theart, and are not to be construed as limitations to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although one or more embodiments of thepresent invention have been described in detail, it should be understoodthat the various changes, substitutions, and alterations could be madehereto without departing from the spirit and scope of the invention.

1-10. (canceled)
 11. A communication device comprising: a powergenerator that converts energy into power; an environmental sensor thatdetects a state of an ambient environment; a wireless communicationcircuit that operates upon receipt of power supplied from the powergenerator; and a controller that controls a transmission interval ofdata which is transmitted from the wireless communication circuit basedon the state of the ambient environment detected by the environmentsensor.
 12. The communication device according to claim 11, furthercomprising at least one timer that outputs a timing signal of a fixedperiod, wherein the controller operates the wireless communicationcircuit at intervals corresponding to a period of the timing signalselected based on the state of the ambient environment detected by theenvironmental sensor, each of the intervals being one of a plurality ofmutually different intervals.
 13. The communication device according toclaim 11, further comprising a plurality of timers that output timingsignals at different periods, wherein the controller selects one of thetiming signals output from each of the plurality of timers based on thestate of the ambient environment detected by the environmental sensor,and operates the wireless communication circuit at intervalscorresponding to the period of the selected timing signal.
 14. Thecommunication device according to claim 11, wherein in a case where thewireless communication circuit is operated at a first interval, thecontroller sets a state of the wireless communication circuit at a timeof non-operation to a standby state in which reactivation is notperformed and power is consumed, and in a case where the wirelesscommunication circuit is operated at a second interval longer than thefirst interval, the controller sets the state of the wirelesscommunication circuit at the time of non-operation to a system off statein which reactivation is performed and power is not consumed.
 15. Thecommunication device according to claim 14, wherein in the case wherethe wireless communication circuit is operated at the second interval,the controller enters the system off state after setting the state ofthe wireless communication circuit at the time of non-operation to thesystem off state, and reactivates the wireless communication circuitafter being reactivated based on a timing signal corresponding to thesecond interval.
 16. The communication device according to claim 11,further comprising a first switch provided on a power supply pathconfigured to supply power to the wireless communication circuit,wherein the controller controls an operation timing of the wirelesscommunication circuit by controlling on and off of the first switch. 17.The communication device according to claim 11, wherein theenvironmental sensor includes at least one of an illuminance sensor anda temperature sensor.
 18. The communication device according to claim11, wherein the power generator includes a solar cell, the environmentalsensor includes an illuminance sensor, and the controller sets anoperating interval of the wireless communication circuit in a case wherean illuminance detected by the illuminance sensor is lower than athreshold to be longer than an operating interval of the wirelesscommunication circuit in a case where an illuminance detected by theillumination sensor is higher than the threshold.
 19. The communicationdevice according to claim 16, further comprising: a capacitor coupled inparallel to the power generator; a second switch provided on at leastone of a pair of power supply lines to which a generated voltage outputfrom the power generator is applied; a first power supply monitor thatcontrols the second switch based on a voltage generated in the pair ofpower supply lines; a third switch provided on a branch line coupled tothe pair of power supply lines; a second power supply monitor thatcontrols the third switch based on a level of a voltage generated in thepair of power supply lines; and a power storage, provided on the branchline, that is coupled and to the power generator when the second switchand the third switch are both turned on; wherein the controller iscoupled to the power generator when the second switch is turned on, andcoupled to the power storage when the third switch is turned on, thewireless communication circuit is coupled to the power generator whenthe first switch and the second switch are both turned on, and coupledto the power storage when the first switch and the third switch are bothturned on.
 20. The communication device according to claim 19, furthercomprising: a first diode coupled in parallel to the second switch; afourth switch that is provided on one of the pair of power supply linesand is turned on and off based on the state of the ambient environmentdetected by the environmental sensor; and a second diode coupled inparallel to the fourth switch so as to face in a direction reverse to adirection of the first diode.